1. Field of the Invention
The present invention relates to a fundus image photographing method and a fundus image photographing apparatus, and particularly, to an aberration correction method that has an adaptive optics function of measuring and correcting an aberration of an eye to be inspected and that is for correcting the aberration according to a situation of acquisition of a photographed image, a fundus image photographing method that can correct an aberration based on the method, and a fundus image photographing apparatus.
2. Description of the Related Art
In recent years, an SLO (Scanning Laser Ophthalmoscope) that two-dimensionally directs a laser beam to the fundus to receive reflected light to form an image and an imaging apparatus that uses interference of low-coherence light are developed as ophthalmic photographing apparatuses. The imaging apparatus using the interference of the low-coherence light is called an OCT (Optical Coherence Tomography), which is particularly used to obtain a tomographic image of the fundus or near the fundus. Various types of the OCT are developed, such as a TD-OCT (Time Domain OCT) and an SD-OCT (Spectral Domain OCT).
Particularly, the resolution is further improving in the ophthalmic photographing apparatuses in recent years, due to a high NA of an illumination laser.
However, the fundus needs to be photographed through optical parts of the eye, such as cornea and crystalline lens. Therefore, the aberration of the cornea and the crystalline lens significantly affects the image quality of the photographed image along with the improvement in the resolution.
Consequently, the research of an AO-SLO and an AO-OCT that include an optical system with an adaptive optics (AO) function for measuring the aberration of the eye to correct the aberration is in progress. For example, “Y. Zhang et al, Optics Express, Vol. 14, No. 10, 15 May 2006” illustrates an example of the AO-OCT. The AO-SLO and the AO-OCT generally measure the wave front of the eye based on a Shack-Hartmann wave front sensor system. The Shack-Hartmann wave front sensor system is a system in which measuring light is directed to the eye, and a CCD camera receives reflected light through a microlens array to measure the wave front. A deformable mirror and a spatial phase modulator are driven to correct the measured wave front. The AO-SLO and the AO-OCT can photograph the fundus through the deformable mirror and the spatial phase modulator to perform high-resolution photographing.
In the AO used in an ophthalmic apparatus, the aberration measured by the wave front sensor is generally modeled by a function such as a Zernike function, and the function is used to calculate a correction amount of a wave front corrector. To correct a complicated shape, the aberration needs to be modeled by a high-order function to calculate the correction amount to control the wave front corrector.
However, the calculation of the correction amount imposes a significantly high calculation load, and an increase in the calculation time is a major problem. Particularly, periodical observation of the diseased part is requested for the ophthalmic apparatus to follow up the illness. Therefore, some reduction in the photographing time is essential to improve the efficiency of the ophthalmic medical treatment.